Ethanol metabolizing Lactobacillus for cancer prevention. Mortality from colorectal cancer (CRC) is second only to that from lung cancer in men and breast cancer in women. Ethanol consumption is a well known risk factor for CRC. Recently, the host ethanol metabolism gene polymorphism has been linked to increased risks of ethanol-associated cancers, mainly esophageal cancer, but also to a lesser degree CRC. Unlike the esophagus, the colon is filled with trillions of bacteria that metabolize ethanol to carcinogenc acetaldehyde. The commensal bacterium Lactobacillus rhamnosus GG has been used for nearly three decades to promote the digestive health and to prevent CRC. However, this bacterium does not metabolize ethanol and thus might have a limited effect against ethanol-associated CRC. By analyzing commensal bacteria for ethanol metabolism we have isolated two L. rhamnosus strains that metabolize ethanol to acetate. These strains not only have all the probiotic benefits of L. rhamnosus GG, but they can also eliminate ethanol and its carcinogenic metabolite acetaldehyde from the host intestine. We hypothesize that ethanol metabolizing L. rhamnosus can reduce the risk of ethanol-associated cancers in the gut. We will pursue two specific aims: (i) study L. rhamnosus genes encoding ethanol metabolism; and (ii) test L. rhamnosus for inhibition of ethanol-associated gut tumorigenesis in mice. Because L. rhamnosus GG has shown some effect against ethanol-unassociated CRC in animals and humans, the proposed study with an ethanol-metabolizing L. rhamnosus will likely lead to the development of a more effective prophylaxis against both ethanol-associated and ethanol-unassociated CRC.